Although contrasting evidence exists in the literature as to the economy of head-loading, there is a notion that head-loading is an extremely economical method of load carriage. This has become known as the 'free ride' hypothesis and, although untested, it is widely accepted. The purpose of this study was to test the 'free ride' hypothesis for head-load carriage among African women by comparing the relative economy of head-loading and back-loading. Twenty-four Xhosa women walked on a level treadmill, attempting to carry loads of between 10% and 70% of their body mass (BM) using both a backpack and a head basket. All 24 women carried at least 25% of their BM in both conditions. The relative economy of load carriage was calculated for loads of 10% to 25% of BM. Results indicated that the 'free ride' was not a generalisable phenomenon, with both methods realising economy scores close to unity (1.04 ± 0.19 and 0.97 ± 0.15 for head-loading and back-loading, respectively). The results did, however, reveal significant individual differences in economy scores and it is suggested that analysis of such individual differences in future may well be instructive in understanding mechanisms associated with greater economy in load carriage.http://www.sajs.co.za

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The purpose of this study was to compare the subjective perceptual responses to both head-loading and back-loading in a group of Xhosa women. Thirty two women were divided into three groups based on their experience of head-loading and walked on a treadmill on two occasions, head-loading and back-loading, at a self selected walking speed for 4 min with a variety of loads until pain or discomfort caused the test to be terminated or a load of 70% body mass was successfully carried. After each workload there was a 1 min rest period during which the women indicated feelings of pain or discomfort in particular areas of the body via visual analogue scales. At the end of each test the women were asked to complete further questionnaires relating to pain and discomfort and on completion of the second test were also asked to compare the two loading conditions. Finally the women were interviewed to establish their history of load carriage and associated pain and discomfort. The data indicate that whilst back-loading was generally associated with more areas of discomfort than head-loading, the pain and discomfort in the neck associated with head-loading was the predominant factor in the termination of tests and that this was independent of head-loading experience. This early termination meant that, on average, the women could carry greater loads on their backs than on their heads. The study suggests that further work needs to be carried out to establish viable alternatives to head-loading for rural dwellers in Africa.

Aim: to quantify the physiological cost of head-load carriage and to examine the 'free ride' hypothesis for head-load carriage in groups of women differing in their experience of headloading.Method: Twenty four Xhosa women (13 experienced head-loaders (EXP), 11 with no experience of headloading (NON)) attempted to carry loads of up to 70% of body mass (BM) on both their heads and backs whilst walking on a treadmill at a self selected walking speed. Expired air was collected throughout. In a second study nine women, members of the British Territorial Army (TA), carriedsimilar loads, again at a self selected speed.Results: Maximum load carried was greater for the back than the head (54.7±15.1% v 40.8±13.2% BM, P<0.0005). Considering study one, head-loading required a greater oxygen rate than back-loading (10.1±2.6 ml.kgbodymass -1 .min -1 v 8.8±2.3 ml.kgbodymass -1 .min -1 , P=0.043, for loads 10-25%BM) regardless of previous head-loading experience (P=0.333). Percentage changes in oxygen consumption associated with head-loading were greater than the proportional load added in both studies but were smaller than the added load for the lighter loads carried on the back in study 1. Allother physiological variables were consistent with changes in oxygen consumption. Conclusion:The data provides no support for the 'free ride' hypothesis for head-loading although there is some evidence of energy saving mechanisms for back-loading at low speed/load combinations. Investigating the large individual variation in response may help in identifying combinations of factors that contribute to improved economy.2

The Extra Load Index (ELI) has been proposed as a suitable method of assessing the relative economy of load carriage systems. The purpose of this study was to determine, based on empirical evidence, that the ELI can accommodate variations in both body composition and added load. Thirty women walked carrying loads of up to 70% BM at self selected walking speeds whilst expired air was collected. In addition each of the women had body composition assessed via DXA. Results show that the ELI is independent of body composition variables, the magnitude of additional loads and the speed of progression. Consequently it is suggested that it represents an appropriate method of comparing load carriage systems in both scientific and commercial arena. Key wordsPhysiology, anthropometry, product design, ergonomics tools and methods word statementWe demonstrate that the Extra Load Index (ELI) is independent of body composition, added load and speed and is therefore an appropriate method to generalise comparisons of load carriage systems. It has the advantage of being easily understood by manufacturers and consumers whilst retaining appropriate scientific precision.